A few important things:

• "It works on my IDE" is NEVER a point to raise an issue.
• Use a spoiler flag as soon as you post code somewhere so that users who didn't solve the kata cannot see it. I put the flag for you this time.
• Please use markdown tags to format your code or it's unreadable
• You must return the result, not print it, it's the same here and in all katas.

About all this and more, I strongly advice you to read carefully this before raising any other issue: https://docs.codewars.com/training/troubleshooting

Not an issue, read about default arguments

I get this error in C# language:
tests/Fixture.cs(16,45): error CS7036: There is no argument given that corresponds to the required formal parameter 'name' of 'Kata.Hello(string)'